There are many paned window implementations, including a core one that was released in 8.4.

http://www.purl.org/tcl/home/man/tcl8.4/TkCmd/panedwindow.html
See also [paned window].
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Here is information on Iwidgets implementation:

[http://incrtcl.sourceforge.net/iwidgets/iwidgets/panedwindow.gif]

Docs can be found at http://incrtcl.sourceforge.net/iwidgets/iwidgets/panedwindow.html (''the example provided may be outdated and fail to work with the latest Tcl/Tk'') and http://purl.org/tcl/home/man/iwidgets3.0/panedwindow.n.html

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Some users with iwidget panedwindows in their apps find that,
when moving to Tk 8.4 ,
their applications are now generating syntax errors.
This is because the Tk panedwindow and iwidgets panedwindow widgets use
the same class - however, they don't have the same bindings.

[Tom Silva] writes on the itcl mailing list:
I use this code-fix in panedwindow.itk, in the Panedwindow constructor,
down near the bottom (just before "eval itk_initialize $args").

  set btags [bindtags $itk_component(hull)]
  if {[set ndx [lsearch -exact $btags Panedwindow]] >= 0} \
  {
    bindtags $itk_component(hull) [lreplace $btags $ndx $ndx IPanedwindow]
  }





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Prompted by an observation by [Bryan Oakley] that, whereas

    [winfo manager $w] forget $w

does what one want for $w-s managed by [pack], [place], and [grid], but
not for panedwindow, [Joe English] offered this "interesting solution":

    set scratch [winfo parent $w].__temp__
    pack $w in $scratch
    pack forget $w
    destroy $scratch 
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[Category Widget] - [Category Command], a part of [Tk] and [incr Widgets]